Oh dear. Well, at least you recognize this as a linear first order differential. It is the confusion on what your integrating factor is that is the problem. Remember, a differential is in linear form when it is written as:
, with an integrating factor equal to .
Rewriting the equation so that it is in linear form we get:
Thus, our integrating factor is . From here you should see how things start to cancel out. If you need more help, post here.